My 2004 XJ8 4.2L w/76k miles is experiencing a strange noise seemingly coming from the the dash area at idle.

It sounds most similar to maybe a failing catalytic converter or if the bearings in the blower motor were failing. Kind of a rattle/grind type of noise. Sometimes it sounds more like boiling water or oil dripping back into the pan.

To answer questions to help narrow it down

1) The noise happens most noticeably at idle - perhaps other times but the noise of the engine drowns it out. It seems to happen in gear and neutral, I'll have to confirm on park or not. I doesn't get louder with RPM.

2) There is no noise with the engine off (so its not a rodent living in the hvac, lol)

3) The noise is pretty quiet overall, the radio and blower motor will drown it out.

4) The noise is hard to pin down location wise. Sometimes is sounds as if it is on the left, sometimes on the right, sometimes down nearer to the transmission/undercarriage, mostly in the center.

5) The noise happens with the hvac off, thus eliminating that as a possibility.

6) Listening underhood, nothing similar is heard or it cannot be heard over the typical engine noise.

Has anybody experienced anything like this? I realize it is a very difficult thing to describe verbally with any accuracy.

Sincerest thanks for any insight.

 

Does it sound like a persistent ticking, like a lifter. Listen outside the car between the rear of the front tire and wheel well area and report back...

Tom

 

It might be the air-con cooling circuit. Low gas pressure or something. When was the gas content last checked on the air con ? Most manufacturers specify about 2 years between checks. Where the gas goes nobody seems to know, but it leaks out somewhere !

 

@Panels - There is a persistent lifter tick. However this noise seems independent of the lifter noise (but perhaps they are related). This may be a different thread but aside from topping off the oil, what remedies are there for noisy lifter(s)? Thank you for your help.

@Fraser Mitchell - Thank you for the suggestion. I will have this checked.

 

I also have a very persistent and sometimes quite loud ticking noise, for you veterans, anything to worry about? My car has 55,000 miles and is a 2004 XJR.

Thanks in advance for any info on this,

Keith

 

Update: After some more driving, I noticed the noise was in fact happening with the engine off. I researched this a bit further and it seems to be a fairly common problem across makes and models when some air gets in the cooling system and gets trapped in the heater core. I have a very slow leak in the thermostat housing and have been topping the coolant occasionally so this makes sense.

I checked the coolant level, then drove the car to warm it up, then loosened the bleed screw on the coolant overflow to vent any air and the noise has stopped. I still need to fix the coolant leak and the problem should be fixed permanently.

Does anyone have a link to the factory recommended or "proper" bleeding procedure for the coolant system, for future reference?

Thanks again to all posters.